Technical Field
The present disclosure relates to the fabrication of integrated circuit MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) devices, and in particular, to strained silicon devices.
Description of the Related Art
Integrated circuits built on silicon substrates typically incorporate field effect transistors (FETs) in which current flows through a semiconducting channel between a source and a drain, in response to a voltage applied to a gate. Strained silicon transistors are MOSFET devices that introduce compressive strain into the silicon substrate to increase mobility of charge carriers in the semiconducting channel. Increasing the charge mobility results in a faster switching response to changes in voltage applied to the gate. One way to introduce strain is to replace bulk silicon in the source and drain regions, or in the channel itself, with an epitaxially-grown silicon compound.
Epitaxial growth refers to growth of a layer on the silicon surface that has a similar crystalline structure to that of the underlying bulk silicon. To prevent discontinuities at the boundary of the epitaxial layer, it is important to perform an “epi pre-clean” step to ensure that the crystalline surface is free of contaminants. The epitaxial source and drain regions can be doped as the epitaxial growth occurs, by introducing impurities in-situ during the epitaxy process step.